I don't have empirical evidence, but I will say that I've noticed I get 3-4 bars sitting in my office now when before it was typically 2-3. That may be coincidental to the update, however.
After updating my SIII to 4.3, I went from no bars ever (except when my phone is sitting just right in a window) to getting a couple now and then in certain spots in my house. Huge improvement for me.